1Switching, impairments, metrics ...Network Switching Technologies, Impairments, and Metrics #32Switching, impairments, metrics ...Outline Basic networking technologies Circuit Switching Packet Switching Statistical Multiplexing Virtual Circuit Switching Network impairments The physical environment impacts network protocols Performance Metrics3Switching, impairments, metrics ...Network Switching TechnologiesInput port 2Line Card BLine CardInterfaceInput Lines Output LinesOutput port 3Line Card CSwitch FabricControlABCDABCD24Switching, impairments, metrics ... Switching transfers information from input ports to output ports Elements of Switches Line cards (multiple interfaces/card) Switch fabric Control (mappings) Management BillingNetwork Switching TechnologiesInput port 2Line Card BOutput port 3Line Card C5Switching, impairments, metrics ...Network Switching Technologies: Circuit Switching On demand call set up Dedicated fixed path Fixed network resources held for call durationEnd-OfficeLong-distanceOfficeLong-distanceOfficeEnd-OfficeTrunksLocal loop6Switching, impairments, metrics ...Network Switching Technologies: Circuit Switching Phases of a call Call establishment Information transfer Call disconnect If no network resources are available the call blocks (fast busy signal) Network resources can be easily defined: e.g., “Voice line”7Switching, impairments, metrics ...Network Switching Technologies: Circuit Switching The Public Switched Telephone Network (PSTN) Dense Wavelength Division (DWDM) Optical Networks Dial-up modems Customers can not use idle channels, unused capacity is wasted8Switching, impairments, metrics ...Network Switching Technologies: Message Switching No Dedicated path Address information is added to the message Store if output port is busy Trade off delay for blocking If message is corrupted then retransmit entire messageStore&ForwardStore&ForwardStore&Forward9Switching, impairments, metrics ...TDM vs Statistical MultiplexingServerDwell time = one time slotUser 1User NServerUser 1User NTDM Statistical Multiplexing If system empty then immediately TX packet at total link rateDelay wait for turn and then TX packet at total link rateLoss arrive and buffer is fullLink Rate in b/sLink Rate in b/s10Switching, impairments, metrics ...TDM vs Statistical Multiplexing Example: Link rate = 1 Mb/s Message size = 5000 bits TDM– Frame size = 10 ms ( 1 Mb/s * 10 ms =10,000 bits)– 10 times slots /frame ( slot time = 1 ms, 1000 bits/slot)– Time to transmit 5000 bit message = 5 slot times @ 1 slot /frame = 50 ms Statistical Multiplexing– Assume arriving message finds the system empty– Time to transmit 5000 bit message = 5000 bits/(1Mb/s) = 5 ms11Switching, impairments, metrics ...Network Switching Technologies: Message Switching If message arrives to empty system then it is transmitted at the FULL LINE RATE Transmission at the FULL LINE RATE is shared among the all the users If a message arrives to a busy system it waitsBufferServerMessageThis is called a Statistical Multiplexer12Switching, impairments, metrics ...Network Switching Technologies: Packet Switching Break up messages into smaller units: Packets The process of “breaking up” larger information units into smaller parts is called: Segmentation or Fragmentation The process of “putting together” smaller parts into larger information units is called: Reassembly Segmentation and Reassembly (SAR) can happen multiple times to the same information stream, or flow13Switching, impairments, metrics ...Network Switching Technologies: Packet SwitchingPacket SwitchForwarding TableInput PortsOutput Ports14Switching, impairments, metrics ...Network Switching Technologies: Packet Switching: Methods Datagram Packet SwitchingConectionless Virtual Circuit Packet SwitchingConnection-oriented15Switching, impairments, metrics ...Network Switching Technologies: Packet Switching --> Datagrams Each packet is treated independently Packets with same destination may take different routes through the network Each nodes makes independent forwarding decisions No call set up is required Nodes keep no “state” information No QoS is guaranteed16Switching, impairments, metrics ...Network Switching Technologies: Packet Switching -->DatagramsTo: John SmithAddressFrom: Jane DoeAddressUser Data insideenvelope17Switching, impairments, metrics ...Network Switching Technologies: Packet Switching --> DatagramsStore&ForwardStore&ForwardStore&ForwardDestination Address Source AddressData 18Switching, impairments, metrics ...How do Packets find there way: Routing and Forwarding1230111Value in arrivingpacket’s headerrouting algorithmlocal forwarding tableheader valueoutput link01000101011110013221Modified from Computer Networking: A Top Down Approach Featuring the Internet, 4nd edition. Jim Kurose, Keith Ross, Addison-Wesley, Copyright 1996-2002, J .F Kurose and K.W. Ross, All Rights ReservedValue related to destination19Switching, impairments, metrics ...Network Switching Technologies: Packet Switching --> DatagramsDatagram is an example of a connectionless serviceInternet Protocol (IP) provides a connectionless service20Switching, impairments, metrics ...Network Switching Technologies: Virtual Circuit Packet Switching Virtual circuit packet switch is: connection oriented Connection oriented does not imply virtual circuits  A “logical connection” is established between the source and destination All packets flow over the same route through the network Packets still “statistically share” link21Switching, impairments, metrics ...Virtual circuits: signaling protocols used to setup, maintain teardown VC used in ATM, frame-relay, X.25applicationtransportnetworkdata linkphysicalapplicationtransportnetworkdata linkphysical1. Initiate call2. incoming call3. Accept call4. Call connected5. Data flow begins6. Receive dataModified from Computer Networking: A Top Down Approach Featuring the Internet, 4nd edition. Jim Kurose, Keith Ross, Addison-Wesley, Copyright 1996-2002, J .F Kurose and K.W. Ross, All Rights ReservedThese are Packet Switches22Switching, impairments, metrics ...Network Switching Technologies: Virtual Circuit Packet Switching Forwarding decisions are made based on a “virtual circuit identifier”